Potentiometer



1965 M. NIRENBERG ETAL 3,

POTENTIOMETER Filed Aug. 28, 1961 \NVENTORS ATTO R N EYS United States Patent Ofifice 3,166,728 Patented Jan. 19, 1965 3,166,723 PUTENTIOMETER Morris Nirenberg, Howard Beach, and Michael Sekerich, Brooklyn, N.Y., assignors to Vogue Instrument Corporation, Brooklyn, N.Y., a corporation of New York Filed Aug. 28, 1961, Ser. No. 134,427 9 Claims. (Cl. 338l44) The present invention relates generally to variable electrical resistance structures, and in particular to an infinite resolution wire wound potentiometer.

Potentiometers are available on the market which comprise a non-metallic cylindrical wire form which has its outer surface formed with a continuous helical groove having mounted therein a helically Wound resistance wire. Theopposite ends of the resistance wire are electrically connected to appropriate terminals and a movable electrical contact is made to successive portions of the resistance wire by a wiper arranged contiguous to the outer surface of the wire form. The wiper underlies and engages the resistance wire and is rotatably mounted, as by being connecteddirectly to a control shaft. Accordingly, the wiper may be rotated into various adjusted positions wherein successive portions of the resistance wire are lifted out of the helical groove and provide an adjustable and stepless output as a function of the adjusted position of the wiper.

Potentiometers of this type, which are particularly suited for use in servo mechanisms, should have a number of essential characteristics including, without limitation, the provision of a truly stepless output, a virtually linear output, and a relatively low order of inductance and capacitance to facilitate use in alternating current circuits. Additionally, and in operation, it is important that the potentiometer produce low noise, be capable of operation at relatively low torque, and have a long life despite the wear incident to the continuous adjustment of the potentiometer and the sliding contact between the wiper and the resistance wire.

Broadly, it is an object of the present invention to provide an improved wire wound potentiometer of the infinite resolution type which is capable of realizing one or more of the aforesaid objectives. Specifically, it is Within the contemplation of the present invention to provide an improved mounting and controlling arrangement for the wiper or brush of a potentiometer such that the wiper will exactly follow the helical path of the resistance wire, thus minimizing sliding or helical error between the wiper and the resistance wire and insuring extremely long wire life, true stepless output, high accuracy and a relatively low order of electrical noise.

In accordance with an illustrative embodiment demonstrating objects and features of the present invention, there is provided an infinite resolution potentiometer which comprises a wire form having a helical groove in which is mounted a helically wound resistance wire. A stationary lead screw extends axially of the resistance wire and projects from the wire form, with the lead screw having a pitch corresponding substantially to the pitch of the helical groove. A follower threadedly engages the lead screw posite ends of the resistance wire respectively, and collector means are electrically connected to the brush for providing a stepless output from the brush. The lead screw, follower and wire form may be machined to an exceptionally high order of accuracy to assure that the Wiper or brush will follow the exact helical path of the resistance wire, thereby providing a stepless output with substantially no sliding or helical error.

The above brief description as well as further objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of a presently preferred, but nonetheless illustrative embodiment in accordance with the present invention, when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is an elevational view of an infinite resolution potentiometer demonstrating features of the present invention, with the cylindrical case or cover sectioned to reveal the contents thereof;

FIG. 2 is a sectional view taken substantially along the line 2-2 of FIG. 1, looking in the direction of the arrows;

FIG. 3 is a sectional view taken substantially along the line 3-3 of FIG. 2, looking in the direction of the arrows; and

FIG. 4 is a sectional view taken substantially along the lines 44 of FIG. 3.

Referring now specifically to the drawings, there is shown a potentiometer Iii which illustrates features of the present invention and includes a housing 12 having spaced mounting or end plates 14, 16 and a cylindrical case or cover 18. The mounting or end plates 14, 16 are formed with peripheral or marginal seats 14a, 16a which receive the adjacent opposite ends of the removable case or cover 18. In a typical construction, the mounting plate 16 and the cover 18 may be fabricated of anodized aluminum or similar lightweight material.

Projecting from the mounting plate 14 internally of the case 18 is a cylindrical wire form 29 which is fabricated of an appropriate non-metallic material having good dimensional stability and a low thermal coemcient of linear expansion, such as a fluoro-carbon. The outer periphery or surface of the cylindrical wire form 20 is provided with a continuous helical groove 22, shown for the purposes of illustration on a greatly exaggerated scale. The helical groove 22, which is precision ground and is of generally V-shaped section (see FIG. 2), receives a heli-v FIGS. 1 and 2). Although only a groove cross-section and is movable therealong in response to being rotated.

which is of V-shaped configuration has been illustrated, it will be appreciated that other cross-sections for the groove 22 are contemplated for accommodating the resistance wire 24. In this illustrative embodiment, the cylindrical wire form 20 is integral with the end or mounting plate 14, but it will be appreciated that it may be fabricated separately therefrom and attached thereto in any appropriate fashion.

, The integral mounting or end plate 14 and wire form 20 support a stationary lead screw 26 which projects from the Wire form 20 toward the mounting or end plate 16 along the longitudinal axis of the wire form. Specifically, and as seen best in FIG. 2, the stationary lead screw 26 includes an externally threaded screw section 26a, an intermediate mounting flange section 26b, and a cylindrical mounting stud section 260. The mounting flange section 26b is disposed within a seat 20a formed in the adjacent end face of the wire form 20, while the mounting stud section 260 is accommodating within a centrally disposed bore 20b formed in the wire form 20 axially thereof and in communication with the seat 20a. The mounting flange section 26b is held within the seat 20a and the mounting stud section 26c is held within the bore 2% in any appropriate fashion, as by attachment to the stepless output terminal 28 which extends axially of the mounting plate 14 and is appropriately shaped for the making of electrical connection thereto at the adjacent outer end of the housing 12.

The screw section 26a of the lead screw 26 carries a follower assembly 30 which includes a follower nut 32 in threaded engagement with the screw section 26b, an insulating block 34 disposed within a peripheral cutout in the follower nut 32 and secured thereto, and a brush or wiper 36 of electrically conductive material secured to the insulating block 34. As seen best in FIG. 1, the brush or wiper 36 includes a mounting section 36a which overlies the insulating block 34, a contact section 36b which extends generally parallel to the longitudinal axis of the wire form 20 and underlies and engages successive portions of the resistance wire 24, and a neck 36c of reduced cross section interconnecting the contact section section 36b and the mounting section 36a. The assembly of the insulating block 34 and the brush or wiper 36 to the follower nut 32 is made by one or more mounting screws 38 which extend through the mounting section 36a of the brush 36 and the insulating block 34 and are received in appropriate tapped holes in the underlying portion of the follower nut 32 (see FIG. 3).

As will subsequently be described, the follower assembly 30 is rotated about and along the lead screw 26 to move the wiper or brush 36 along a helical adjustment path coextensive with the resistance wire 24 such that the transverse segment of the contact section 36b underlying the resistance wire 24 may make continuous contact with successive portions of the resistance wire 24. The transverse segment of the contact section 36b underlying the resistance wire 24 may be slightly grooved or notched to preclude sidewise movement between the contact section 36b and the resistance wire 24. However, it will be appreciated that the provision of such groove or notch is optional, since the pitch of the lead screw section 26a and the pitch of the helical groove 22 is the same and may be held toextremely close tolerances relative to each other due to the precision grinding or cutting of the lead screw 26 and the wire groove 22. In a typical assembly, the Wiper or brush 36 is fabricated of a resilient alloy, such as beryllium-copper, with the reduced neck 36c allowing the contact section 36b to flex relative to the mounting section 36a. The contact section 360 is bowed on an arc corresponding to the outer periphery of the wire form 20 such as not to present any sharp discontinuities to the resistance wire 24 as the contact section 36b moves therebeneath. The

contact section 36b may be fabricated of or plated with a precious metal, such as a platinum alloy.

A control assembly or mechanism is operatively connected to the follower nut 32' of the follower assembly 30 for rotating the follower nut on the lead screw 26 to move the contact section 36b on the brush or Wiper 36 along the helical adjustment path in electrical contact with the resistance Wire 24. This control assembly or mechanism includes a control shaft 40 journalled on the mounting or end plate 16 and extending axially of and toward the lead screw 26. The control shaft 40 includes a bearing section which is received within an integral sleeve bearing 16b formed on the mounting or end plate 16 and a control section 40b which projects externally of the sleeve bearing 16b. Upon mountingin an environment structure, as by the use of the mounting nuts 42, 44, the control section 4012 of the control shaft 40 may be connected to an appropriate input for the potentiometer 10.

At its inner end, the bearing section 40a of the controlshaft 40 carries a control head 46 which is secured to the bearing section 46a in any appropriate fashion, as by one or more screws 48 which project radially through a mounting flange 46a integral with the control head 46 and are engaged with the adjacent end of the bearing section 40a. The mounting flange 46a of the control head 46 is accommodated within a seat formed in the inner face of the end plate 16 and cooper-ates with a locking ring 50 which is received within a circumferential groove 46c formed in the control shaft 40 to main tain the control shaft against endwise displacement. It will be appreciated that other arrangements may be provided for mounting the control shaft 40 on the end plate 16 of the housing 12 in axial alignment with the lead screw 26. The control head 46 carries a drive finger 52 which projects from the control head 46 toward the follower nut 32 at a location laterally offset from and parallel to the longitudinal axis of the head screw 26. The drive finger 52 is slidably engaged in a peripheral cutout 32a in the follower nut 32. Specifically, and as seen best in FIGS. 3 and 4, the follower nut 32 is formed with internal cavities 32b, 32c which project in opposite directions from the peripheral cutout 32a, with the opposite walls of the cavities being formed with opposed pairs of holes, such as indicated at 32d, 32e (see FIG. 4). Any appropriate plastic is molded into the cavities and is firmly embedded therein due to the integral extensions thereof which project through the opposed pairs of holes 32d, 32c and provide integral mounting studs or pins. The molded plastic in the internal cavities 32b, 320 provides an insulating insert 54 which is virtually integral with the follower nut 32. The insulating insert 54 is formed with a cut-out or slot 54a within the confines of the slot or cut-out 32a. The slot 54a receives the drive finger 52 which may be milled with opposed flats therealong. The spacing between the flats corresponds approximately to the spacing between the opposite walls of the cut-out 54a to provide an intimate but sliding contact therebetween. Conveniently, the insulating insert 54 may be fabricated of a plastic which has self-lubricating properties to assure the provision of a substantially frictionless driving contact between the drive finger 52 and the follower nut 32.

Collector means are electrically and rotatably connected to the brush .36 for providing a tapoff and stepless output therefrom. In this illustrative embodiment, the collector means includes a rotatable terminal 56 which is riveted or otherwise secured to the control head 46 and is electrically isolated therefrom by a surrounding insulating sleeve 58. The rotatable terminal 56 is located radially outwardly of the longitudinal center of the lead screw 26 and carries a resilient collector arm 60 which extends radially toward the center of the lead screw 26 where the arm 60 terminates in a collector button 60a which is in axial contact with the lead screw 26. Conveniently, the lead screw 26 serves as a central electrode about which the collector arm 60 turns in response to rotation of the con trol head 46. A flexible jumper wire 62 is electrically connected to the brush 36 and to the rotatable terminal 56. As seen bestin FIGS. 1 and 2, the flexible jumper 62 is folded into a generally U-shaped configuration to permit the unobstructed axial travel of the follower nut 32 on the lead screw 26, with oneend of the jumper wire 2 2%) (see FIGS. 1 and 2) at location somewhat radially and inwardlyof the outer periphery of the wire form 20. The terminal strip 64 has an electrical connection to the outer end of the resistance Wire 24 contiguous to the mounting or end plate 14 (see FIG. 2) and is electrically connected to a terminal 68 contiguous to the terminal 28.

The terminal strip 66 has an electrical connection to the inner end of the resistance wire 24 remote from the end mounting plate 14 and is electrically connected to a further terminal 70 (see FIG. 2) which is contiguous to the other terminals 28, 68.

Mechanical end stops are provided to limit the traverse of the follower nut 32 on the lead screw 26 and the corresponding traverse of the brush 36 along the helical adjustment path relative to the resistance wire 24. In this illustrative embodiment, the follower nut 32 is provided with movable stop pins 72, 74 which project from the opposite faces thereof. The stop pin 72 limits the travel of the follower nut 32 to the right in FIGS. 1 and 2, while the stop pin 74 limits the travel of the follower nut 32 to the left in FIGS. 1 and 2. Specifically, the movable stop pin 72 cooperates with a stationary end stop 76 which is formed integral with or secured to the intermediate mounting flange section 26]) of the lead screw 26 at a location radially disposed to contact the movable stop pin 72. The movable stop pin 74 in turn cooperates with a radially projecting stop finger 78 which is mounted on the lead screw 26 adjacent the free end thereof by a centrally extending mounting bolt which is received in an axial tapped hole in the lead screw section 260:. The head of the mounting bolt 80 conveniently serves as the central electrode in contact with the collector button 60d of the radially extending resilient collector arm 60, as seen best in FIG. 2.

A typical sequence of operations will now be described in order to facilitate a more thorough understanding of the invention:

When the potentiometer is incorporated into an operating environment or system, and an input is applied to the control section 40b of the control shaft 40, either manually or automatically, rotation of the control shaft 40 will cause a corresponding rotation of the controlhead 46 and of the drive finger 52. The drive finger 52, due to its coupling with the follower nut 32, will cause the same to rotate about and traverse along the lead'screw section 26a thereby imparting a corresponding motion topthe fol lower assembly 30 and in particular to the brush 36.1 The segment of the contact section 361) of the brush 36 which underlies the resistance wire 24 will move in a helical adjustment path corresponding to the pitch of the lead screw section 26a and to the comparable pitch of the groove 22 thereby providing a stepless output at the terminal 28 which will be a function. of the relative position of the contact section 3611 along the resistance wire 24. The contact pressure of the brush 36 may be established to provide relatively low frictional contact with the resistance wire 24 and to achieve the necessary electrical tapoff, yet assures long life and relatively low wear. Further, since the brush or wiper 36 follows the exact helical path of the resistance wire 24 there will be a minimum sliding or helical error between the brush 36 and the resistance wire 24. By appropriate selection of materials and controls in manufacturing tolerances, a high order of accuracy may be obtained for the output from potentiometer and optimum of mechanical and operating conditions may be established for this product.

A latitude of modification, change and substitution is intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

What we claim is:

I 1. An infinite resolution potentiometer comprising spaced mounting members, a wire form having an outer surface provided with a helical groove and projecting inwardly of one of said mounting members, a helically Wound resistance wire mounted within said groove, a stationary lead screw extending axially of said resistance wire and projecting outwardly from said wire form toward the other of said mounting members, a follower threadedly engaging said lead screw and movable therealong in response to being rotated, a brush underlying said resistance wire in electrical contact therewith and arranged to lift successive portions of said resistance wire from within said groove, means mounting said brush on said follower for movement therewith along a helical adjustment path such that said brush makes contact with successive portions of said resistance wire, and rotatable control means operatively connected to said follower for rotating the same, said control means including a control shaft journalled on the other of said mounting members and extending axially of and toward said lead screw and drive means carried on said control shaft and slidably coupled to said follower for rotating said follower.

2. An infinite resolution potentiometer according to claim 1 wherein said follower includes an insert of insulating material formed with a peripheral slot and said drive means includes a drive finger extending parallel to said lead screw at a location laterally spaced therefrom, said drive finger projecting through said slot and being in sliding contact with said insert.

3. An infinite resolution potentiometer according to claim l'including movable stops on said follower and stationary stops on said wire form and said lead screw respectively, said movable and static-nary stops being arranged in relation to each other to establish end limits for the axial movement of said follower on said lead screw.

4. An infinite resolution potentiometer comprising spaced mounting members, a wire fo-rm having an outer surface provided with a helical groove and projecting inwardly of one of said mounting members, a helically wound resistance wire mounted within said groove, a stationary lead screw extending axially of said resistance wire and projecting outwardly from said wire form toward theother of said mounting members, a follower threadedly engaging said lead screw and movable therealong in response to being rotated, a brush underlying said resistance wire in electrical contact therewith and arranged to lift successive portions of said resistance wire from within said groove, means mounting said brush on said follower for movement therewith along a helical adjustment path such that said brush makes contact with successive portions of said resistance wire, rotatable control means operatively connected to said follower for rotating the same, said control means including a control shaft journalled on the other of said mounting members and extending axially of and toward said lead screw and drive-means carried on said control shaft and slidably coupled to said follower for rotating said follower, terminal means electrically connected to the opposite ends of said resistance wire respectively, and collector means electrically connected to said brush for providing a stepless output from said brush.

5. An infinite resolution potentiometer comprising spaced mounting members, a wire form having an outer surface formed with a helical groove and projecting inward-1y of one of said mounting members, a helically wound resistance wire mounted within said groove, a stationary lead screw extending axially of said resistance wire and projecting outwardly from said wire form toward the other of said mounting members, a follower threadedly engaging said lead screw and movable therealong in response to being rotated, a brush underlying said resistance wire in electrical contact therewith and arranged'to lift successive portions of said resistance wire from within said groove, means mounting said brush on said follower for movement therewith such that said brush makes contact with successive portions of said resistance wire, rotatable control means operatively connected to said follower for rotating the same, terminal means electrically connected to the opposite ends of said resistance wire respectively, and collector means electrically connected to said brush for providing a stepless output from said brush, said collector means including a rotatable terminal on said control means, a flexible jumper electrically connecting said brush to said rotatable terminal, a central electrode extending axially of and through said lead screw and providing a stationary terminal for said stepless output, and a resilient collector arm mounted on said control means and electrically connected to said rotatable terminal, said collector arm being in contact with said central electrode and turning thereabout during rotation of said control means.

6. An infinite resolution potentiometer comprising spaced mounting members, a wire form having an outer surface provided with a helical groove and projecting inwardly of one of said mounting members, a helically Wound resistance wire mounted within said groove, a stationary lead screw extending axially of said resistance wire and projecting outwardly from said Wire form to- Ward the other of 'said mounting members, said lead screwhaving a pitch corresponding substantially to the pitch of said helical groove, a follower threadedly engaging said lead screw and movable therealong in response to being rotated, a brush underlying said resistance wire in electrical contact therewith and arranged to lift successive portion of said resistance wire from within said groove, means mounting said brush on said follower for movement therewith such that said brush makes contact with successive portions of said resistance wire, rotatable control means operatively connected to said follower for rotating the same, said control means including a control shaft journalled on the other of said mounting means and extending axially of and toward said lead screw and drive means carried on said control shaft and slidably coupled to said follower for rotating said follower, terminal means electrically connected to the opposite ends of said resistance wire respectively, and collector means electrically connected to said brush for providing a stepless output from said brush, said collector means including a rotatable terminal on said control means, a flexible jumper electrically connecting said brush to said rotatable terminal, a central electrode exdrive means includes a drive finger extending parallel to said lead screw at a location laterally spaced therefrom,

said drive finger projecting through saidslot and being in said groove, meansoperatively connected to the opposite ends of said resistance wire for anchoring the same withinsaid groove, a stationary lead screw extending axially of said resistance wire and projecting from said wire form, said lead screw having a pitch corresponding substantially to the pitch of said helical groove, a follower threadedly engaging said lead screw and movable therealong in response to being rotated, a brush underlying said resistance wire in electrical contact therewith and arranged to lift successive portions of said resistance wire from within said groove, means mounting said brush on'said follower for movement therewith such that said brush makes contact with successive portions of said resistance wire, rotatable control means operatively connected to said follower for rotating the same, terminal meanselectrically connected to the opposite ends of said resistance wire respectively, and collector means electritending axially of and through said lead screw and pro-.

cally connected to said brush for providing a stepless output from said brush, said collector means including a rotatable terminal on said control means, a flexible jumper electrically connecting said brush to said rotatable terminal, a central electrode extending axially of and through said lead screw and providing a stationary terminal for said stepless output, and a resilient collector arm mounted on said control means and electrically connected to said rotatable terminal, said collector arm being in contact with said central electrode and turning thereabout during rotation of said control means.

References Cited in the file of this patent UNITED STATES PATENTS 2,773,966 Mastropole Dec. 11, 1956 2,813,182 Van Alen Nov. 12, 1957 2,839,643 Vercesi June 17, 1958 2,871,326 Weidenman et al. Jan. 27, 1959 

1. AN INFINITE RESOLUTION POTENTIOMETER COMPRISING SPACED MOUNTING MEMBERS, A WIRE FORM HAVING AN OUTER SURFACE PROVIDED WITH A HELICAL GROOVE AND PROJECTING INWARDLY OF ONE OF SAID MOUNTING MEMBERS, A HELICALLY WOUND RESISTANCE WIRE MOUNTED WITHIN SAID GROOVE, A STATIONARY LEAD SCREW EXTENDING AXIALLY OF SAID RESISTANCE WIRE AND PROJECTING OUTWARDLY FROM SAID WIRE FORM TOWARD THE OTHER OF SAID MOUNTING MEMBERS, A FOLLOWER THREADEDLY ENGAGING SAID LEAD SCREW AND MOVABLE THEREALONG IN RESPONSE TO BRING ROTATED, A BRUSH UNDERLYING SAID RESISTANCE WIRE IN ELECTRICAL CONTACT THEREWITH AND ARRANGED TO LIFT SUCCESSIVE PORTIONS OF SAID RESISTANCE 